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As part of the national plan to minimize unemployment during the 

 great depression of the 1930's the South Carolina Public Service 

 Authority was formed for the purpose of building a large dam, water 

 supply, flood control, navigation lock, recreation and employment 

 opportunity complex. Cost-benefit analysis was needed to show that 

 the project merited the loan of Federal funds. The construction com- 

 plex is referred to as the Santee-Cooper project. 



In 1967 a study to check on the effectiveness of a cost-benefit analysis 

 made 25 years previously was undertaken. Part of this analysis re- 

 vealed that as a result of construction and hydraulic rerouting of 

 rivers the silting in Charleston Harbor increased from what was 

 estimated at $18,000 annually to an actual cost of over $2,029,756 

 annually. For every year in the future that the hydraulic regime of 

 the harbor is not restored to a more suitable mode t)f circulation there 

 will be a dredging cost of roughly the same magnitude incurred. 



The diversion of the Santee River into the Cooper River constituted 

 a remarkable engineering experiment. The designers of the diversion 

 apparently foresaw no adverse effects. To the contrary, they felt that 

 the effects of the added flow would be to flush out the harbor and pre- 

 vent any serious pollution from ever occurring. As a result, the dis- 

 covery that the shoaling rates were increasing in the harbor apparently 

 came as a complete surprise to everyone. By 1947 the Corps of Engi- 

 neers was undertaking model studies to try to determine a solution to 

 the problem. 



The finding of the Corps in their mod'el studies at Vicksburg, Miss., 

 indicated that the increased flow into the harbor area had created a 

 partially mixed estuary. That is, the ratio of freshwater to salt water 

 in the harbor area was such that a definite interface developed which 

 moved longitudinally up and down with the tide. The dense saltwater 

 was overlain by the freshwater inflow. As the freshwater flow in- 

 creased to 15,000 c.f.s., the bottom flood currents became greater in 

 duration over the bottom ebb currents. The effect was to create a net 

 upstream movement of the bottom currents in the saline region of 

 the harbor area, a condition which created a trap at the bottom of 

 the estuary preventing the movement of settling materials out to sea. 



At about the same time the Santee-Cooper project began operations, 

 the project depth of the Charleston Harbor was changed from 30 

 feet to 35 feet. This further complicated the dredging problem for two 

 reasons: first, the Corps had 5 additional feet of depth to maintain 

 and second, the dredging itself loosened the accumulated silt out- 

 side of the shipping channels and allowed it to slip into the channels. 

 The Corps maintained, however, that the natural depth of the Charles- 

 ton Harbor had exceeded 35 feet, and that the greater project depth 

 in itself would not have constituted much of a problem. 



From its study of the shoaling problem in the Charleston Harbor, 

 the Corps estimated that the Santee-Cooper project was responsible 

 for approximately 85 percent of the shoaling in the harbor. The rest, 

 they said, would have occurred without the project. 



In 1965, dredging by the Corps was done at a cost of $2,237,949. It 

 was estimated by the Corps that commercial shippers spent $100,000 

 on dredging operations w^hile the Navy spent $50,000. Assigning 85 

 percent of this cost of the Santee-Cooper project, a negative benefit of 

 $2,029,756 was attributed to operation of the project in 1965. 



